Aminoglycoside antibiotics are used in more than 3 million patients annually for eradication of gram negative infections at an annual cost of more than $109 million. Damage to the kidney, nephrotoxicity, is a common occurrence being noted in at least 2 to 10% of patients treated. Although much is known about the physiology, pharmacology and pathology of aminoglycoside nephrotoxicity, little is known about the metabolic and biochemical basis for this important clinical disorder. This project proposes a series of studies with the overall goal of establishing the biochemical basis for aminoglycoside nephrotoxicity. The hypothesis to be tested is that aminoglycoside toxicity is determined by: (1) cellular uptake of aminoglycosides; (2) accumulation of aminoglycosides in lysosomes and (3) inhibition of lysosomal phospholipases, resulting in formation of intralysosomal multilamellar bodies and ultimate interference with normal lysosomal function. Specific objectives include (1) isolation and characterization of multilamellar bodies from the kidney of aminoglycoside-toxic rats; (2) isolation of lysosomal phospholipases from rat kidney, fibroblasts and Madin Darby canine kidney (MDCK) cells and determination of inhibitory effects of various aminoglycoside antibiotics; (3) determination of the intralysosomal concentration of aminoglycosides as a function of time in kidney, cultured fibroblasts and MDCK cells; (4) establish correlation between measures of toxicity versus intralysosomal concentration of aminoglycosides and ability of aminoglycosides to block lysosomal phospholipases; (5) isolate and purify kidney phospholipase A to homogeneity and study precise mechanisms of aminoglycoside inhibition.